Entry, transport and absorption of hydrogen in low-temperature plasma nitrided austenitic stainless steel

Plasma nitriding of ASTM 316Ti steel at 425 degreesC for up to 30 h produce d nitrogen expanded austenite phase with up to 39 at.% N. The 40-mum thick membranes of nitrided and unnitrided steel were charged with hydrogen by ga lvanostatic cathodic polarisation in 0.1 M NaOH at 25 degreesC and the hydr ogen permeation and desorption were studied by the electrochemical techniqu e. Nitriding decreased the hydrogen permeation rate. Diffusivity of hydroge n in the nitrided layer was higher than that in the unnitrided steel, and t his layer trapped hydrogen more intensely. However, the concentration of th e diffusible hydrogen in the nitrided layer was lower than that in the unni trided steel. As a result, the absorption of hydrogen by the steel substrat e was diminished. (C) 2001 Acta Materialia Inc. Published by Elsevier Scien ce Ltd. All rights reserved.